Method of providing paraffin scrapers on sucker rods



May 17, 1966 G. E. ELL 3,251,919

METHOD OF PROVIDING PARAFFIN SCRAPERS ON SUCKER RODS 3 Sheets-Sheet 1 Original Filed Jan. 30, 1961 INVENTOR.

GEORGE E. ELL

ATTORNEYS May 17, 1966 G. E. ELL 3,251,919

METHOD OF PROVIDING PARAFFIN SCRAPERS 0N SUCKER RODS Original Filed Jan. 30, 1961 3 Sheets-Sheet 2 FIG. 3A FIG. 3

I N VEN TOR. GEORGE E. ELL

Mf/nb ATTORNEYS May 17, 1966 G. E. ELL 3,251,919

METHOD OF PROVIDING PARAFFIN SCRAPERS ON SUCKER RODS Original Filed Jan. 30, 1961 3 Sheets-Sheet 5 INVENTOR. GEORGE E. E LL ATTORNEYS United States Patent 3 251 919 METHOD OF PROVIIIING PARAFFIN SCRAPERS 0N SUCKER RODS George E. Ell, Fort Worth, Tex., assignor to Liberty ManufacturingiCompany of Texas, Fort Worth, Tex.,

a corporation of Texas Original application Jan. 30, 1961, Ser. No. 85,604.

Divided and this application July 30, 1962, Ser. No.

1 Claim. (Cl. 264251) This is a divisional application of an application by the same inventor entitled Pa'rafiin Scraper, Serial Number 85,604, filed January 30, 1961, and now alb andonecl.

This invention relates to paraffin scrapers. More particularly, the invention relates to plastic paraffin scrapers and includes methods of molding plastic paraffin scrapers directly onto sucker rods.

One of the difficult problems encountered in the production of crude oil from pumping Wells is that of parafiin accumulation within the tubing string. At bottom hole temperatures paraffin contained in crude oil is in a liquid form. When the liquid crude oil is pumped to the sun face, areas are reached within the tubing wherein the produced crude oil is lowered in temperature to the point wherein solidification of the paraffin occurs. After a suflicient length of time parafiin may solidify and adhere to the walls of the tubing and build up to such an extent that the tubing is completely sealed, preventing the passage of pumped crude oil up through the tubing to the surface. This, of course, eliminates the usefulness of the Well to produce crude oil, and requires that the tubing be pulled and cleansed of the parafiin or replaced with tubing free of parafiin.

To overcome this difficulty paraffin scrapers have been devised to be afiixed to the sucker rods which actuate with the tubing. Typically, the parafiin scrapers are spaced a distance apart less than the stroke length of the pumping unit which reciprocates the sucker rods. Paraffin scrapers are affixed to the sucker rods and are of a configuration to closely adhere to the interior diameter of the tubing and scrape loose the parafiin that has accumulated on the interior walls of the tubing. The most commonly used type of parafiin scrapers are those made of metal. These metal scrapers are usually welded to the sucker rods in a shop and transported to the well for insertion. When it is necessary to apply parafiin scrapers to wells already in production, the difficult and time consuming tasks are encountered of pulling the rods from the well, loading them on trucks, and transporting them to a fabrication shop where the metal parafiin scrapers are attached, and transporting the rods back to the well for insertion into the well. One object of this invention is to provide a means whereby paraflin scrapers may be applied directly and speedily to sucker rods at the well site, and in a manner wherein welding is not required.

As previously stated, parafiin scrapers most commonly used in the petroleum industry at the present time are made of metal. In practice these metal scrapers rub on the interior Walls of the tubing as the sucker rods actuate up and down within the tubing to pump oil. The metal to-metal wear of the paraffin scrapers against the interior walls of the tubing naturally constitutes a high friction drag and thus a power loss in well pumping, and in addition, causes a wearing away of the tubing by the effect of attrition of the scrapers. Another object of this invention is to provide parafiin scrapers of a plastic material having a greatly improved coefficient of friction so that the total energy required to pump a well is reduced,

3,251,919 Patented May 17, 1966 "ice ers themselves. The use of plastic as a material for the application of paraffin scrapers eliminates all of these difficulties encountered in the use of metal paraflin scrap- EIS.

This invention may be described as a method of directly molding plastic paraffin scrapers to sucker rods. More particularly, but not by way of limitation, this invention may be defined as a method of providing a series of paraffin scrapers on a sucker rod including the steps of positioning a first portion of the rod in a surface preparation cabinet, treating the first portion within the cabinet to remove any scale or other material so as to provide a clean surface, moving the sucker rod so that the cleaned portion is positioned in a'mold, at the same time moving a new portion of the sucker rod into the cleaning cabinet, injection molding a plastic parafiin scraper onto the cleaned portion of the sucker rod in the mold while at the same time cleaning a new portion in the cleaning cabinet, again moving the sucker rod so that the newly cleaned portion is within the mold to receive the molding of a paraflin scraper thereon and at the same time cleaning an additional new portion in the cleaning cabinet, and repeating the steps until the sucker rod is fully provided with spaced molded parafiin scrapers.

Itis, therefore, an object of this invention to provide a means whereby paraffin scrapers may be applied directly to sucker rods at the well site Without the necessity of transporting the rods to a fabrication shop.

Another obje'ctof this invention is to provide paraffin scrapers directly molded to sucker rods which have the advantage of being light in Weight, having an improved coefficient of friction, resistance to corosion, and are nonporous so that paraffin will not readily adhere to the surfaces of the parafiin scrapers.

These and other objects, and a better understanding of the invention may be had by referring to the following description and claims, taken in conjunction with the attached drawing in which:

FIGURE 1 is a top view of a truck having mounted thereon the components necessary to practice the principles of this invention to the direct application of plastic parafiin scrapers to sucker rods.

FIGURE 2 is a side View of the truck of FIGURE 1, showing the relative position of the components neces sary for the direct application of plastic paraffin scrapers to sucker rods.

FIGURE 3A is a side view of one configuration of a plastic paraffin scraper directly molded to a sucker rod by the principles of this invention.

FIGURE 33 is an end view of the plastic paraflin scraper of FIGURE 3A.

FIGURE 4A is a side view of a parafiin scraper directly molded to a sucker rod by the principles of this invention. This paraffin scraper configuration requires the conjoint use of rod rotational devices located at the well surface.

FIGURE 4B is an end view of the plastic paraffin scraper of FIGURE 4A.

FIGURE 5A is a side View of a paraffin scraper directly molded to a sucker rod by the principles of this invention, showing an improved and novel design wherein no rotational devices are required to accomplish complete removal of parafiin from the full circumference of g the interior of tubing, and wherein no rotational torque is applied to the sucker rod by the movement of the paraiiin scraper through fiuid contained in the tubing.

FIGURE 58 is an end view of the plastic paratfin scraper of FIGURE 5A.

FIGURE 6 is a side view of a premolded plastic parafiin scraper half, having a spiral blade integrally formed therewith.

FIGURE 7 is a side view of the premolded plastic parafiin scraper half of FIGURE 6, adaptable for thermofusing to a sucker rod.

FIGURE 8 is a side view of an identical mating half of the premolded plastic parafiin scraper half of FIG- URE 7 FIGURE 9 is a partial cross-sectional view taken along the line 99 of FIGURE 6, showing the provision of grooved gripping lugs on the internal diameter of the premolded plastic parafiin scraper halves.

FIGURE 10 is a cross-sectional view taken along the line 10-10 of FIGURES 7 and 8 as the premolded plastic parafiin scraper halves appear after having been thermofused to a sucker rod.

FIGURE 11 is likewise a cross-sectional view taken along the line 11-11 of FIGURES 7 and 8, showing the premolded plastic parafiin scraper halves of FIGURES 7 and 8, after having been thermofused to a sucker rod.

Referring now to the drawings in first of FIGURE 1, a truck 19 is shown, having an arrangement of equipment according to the principles of this invention, whereby plastic parafiin scrapers may be applied directly to sucker rods. Many types of paraifin scrapers have been suggested by others. Included in the suggested types of parafiin scrapers are all manner of metallic devices adaptable for affixing under spring tension to sucker rods or welding to the sucker rods. Others have suggested plastic type paraflin scrapers having integrally formed metallic clips adaptable for gripping the surfaces of the sucker rods. These types of paraffin scrapers have proved satisfactory, but have certain disadvantages which are overcome according to the principles of this invention.

One of the great problems of presently used types of plastic paraffin scrapers is that the scrapers, if attached by spring pressure or tension to the sucker rods, become loosened fromthe sucker rods and slip up and down on the rods rather than move with the rods to dislodge accumulated paraffin from tubing walls.

Another commonly used method of afiixing metallic scrapers to sucker rods includes bending split metal rings or bands around the sucker rods which are then welded together. The bands are compressed to provide con tinuous contact with the circumference of the rods. The metallic paraffin scraper is attached to the metallic bands, usually at the rate of two bands per parafiin scraper. Sucker rods must withstand great physical loads in their duty of reciprocative transmission of energy from a surface positioned pumping unit to a pump in the bottom of a well. To insure long service life sucker'rods are con structed of high quality steel and are very carefully normalized during the manufacturing process to make sure that all internal stresses are eliminated. If, for any reason, a sucker rod is heated excessively during the process of welding these bands around the rod, such as the welding arc contacting the rod surface, there is danger that an area of internal stress will be developed in the sucker rod, weakening the rod and shortening its service life. When metallic scrapers are applied according to this method the rodsmust be taken to a shop. This means that the rods must be loaded and unloaded from a truck in the process of hauling them to and from the fabrication shop.

To overcome disadvantages of the present systems of applying paraffin scrapers to sucker rods a novel method has been developed wherein all of the equipment necessary to apply parafiin scrapers may be mounted on truck 18. It is not intended to be implied that the principles of this invention are limited to the practice wherein the equipment necessary to accomplish the results of the invention are only mounted on trucks. It is within the purview of the invention that it may be practiced equally as Well in a shop or factory location, but a novel element of the invention is the portable means in which it may be accomplished, and the invention will be described by way of example, as it is practiced by such portable means.

Whereas, in the past, as previously mentioned, paraffin scrapers have either been welded around the sucker rods or affixed to rods under spring tension, an important novel element of this invention is a process whereby parafiin scrapers may be molded directly to the sucker rods.

Mounted on truck 10 are several items of equipment ineluding a surface preparation cabinet 12, a plastic molding machine 14, a plastic storage tank 16, air compressor equipment 18, electrical generating equipment 20, and a sucker rod roller conveyor 22. Not shown are sand tanks, water tanks and detergent tanks which may be positioned in convenient places on the truck bed, or supported underneath the bed of the vehicle. Plasticstorage tank 16 serves as a storage hopper or bin for granulated plastic raw material. The granulated plastic material flows from plastic storage tank 16 into plastic molding machine 14. f

Shown positioned on sucker rod roller conveyors 22 is a sucker rod 23 as it would appear during the process of receiving the application of paraflin scrapers.

Sucker rod roller conveyors 22 are shown only in their partial length in FIGURE 1. In practice they extend out approximately twenty to twenty-five feet in each direction from truck 10, so that the full length of a typical twenty-five foot sucker rod may be supported on the roller conveyors 22 as the sucker rod passes through the equipment by which parafiin scrapers are applied. Roller conveyors 22 are demountable so that they may be removed for hauling.

Generally, plastic parafiin scrapers are afiixed to sucker rods according to the principles of this invention by directly injection molding. In order to provide sufiicient bonding between the injected molded scraper and the sucker rod 23, the area on the sucker rod wherein the scraper is to be applied must first be thoroughly prepared to effect a bonding of the injected molded scraper to the rod. This surface preparation is accomplished in surface preparation cabinet 12. Openings in the surface preparation cabinet 12 permits the sucker rod 23 to pass through the cabinet 12 so that the sucker rod 23can be stopped in a position wherein the area of the rod to receive the first paraffin scraper is within the cabinet 12. Although the specific sequence by which the suiface is prepared may be varied in innumerable ways, the most eflicient method according to' the principles of this invention is to first wash the area of the sucker rod 23 to receive the plastic paraflin scraper with hot water and a detergent. This removes all attached oil and parafiin materials. The area to receive the plastic parafiin scraper is next sandblasted to dislodge any scale, rust, or other foreign materials which may have adhered to the surface. The area to receive the scraper then is rinsed with steam to remove all of the particles dislodged by the sandblastmg, and to prepare a thoroughly clean surface of exposed metal to receive the plastic paraflin scraper. After an area of the sucker rod 23 which is to receive a parafiin scraper is thoroughly prepared in the surface preparation cabinet 12, the sucker rod 23 is moved on the roller conveyor 22, so that the prepared area to receive the paraffin scraper is encompassed within injection molding machine 14.. Segments of a mold Within injection molding machine 14 move around the sucker rod 23 to encompass a portion of the length of the rod. When the mold is ready to receive the plastic material which will formulate the parafiin scraper, the mold defines an area of the ultimately. desired scraper configuration which will be described in greaterdetail subsequently. Granulated plastic material is injected into the mold 14 from storage tank 16. Under heat and pressure the injected thermoplastic material is formed onto the cleansed surface of the sucker rod 23. At the same time the entire cavity surrounding the sucker rod 23 is filled with the thermoplastic material. As soon as the material has been injected and heated to the proper temperature by electrical energy supplied by electrical generating equipment 20, the mold is cooled, and upon cooling the thermoplastic material becomes a solid forming a plastic paraflin scraper permanently formed around the sucker rod. The granular plastic material is injected into the mold and is subjected to a temperature of from approximately 600 to 660 Fahrenheit at a pressure of from approxiamtely 2,000 to 30,000 pounds per square inch. The combina tion of heat and pressure transforms the granular plastic material into a pliable and formable consistency so that the plastic material is caused to conform to the internal configuration of the mold. The full mold, is'in-stantly cooled by the injection of water into a cooling jacket surrounding the mold. This transforms the plastic into a solid state. During solidification the plastic material shrinks around the sucker rod 23, forming a tight bond so that to loosen the finished paratfin scraper from the sucker rod would require returning the plastic paraffin scraper to the plastic transformation temperature range. A plastic paraffin scraper 24 is shown having been directly molded to sucker rod 23.

While a paraflin scraper 24 is being formed on the sucker rod 23 in molding machine 14, the next area to receive a parafiin scraper 24 is being prepared in the surface preparation cabinet 12. The equipment is designed such that the surface preparation requires approximately the same time as is required to mold a paraflin scraper 24 on the sucker rod 23 at the previously prepared area. The total time required to mold a plastic parafiin scraper to the sucker rod is approximately two minutes.

After the plastic paraflin scrapers 24 have been molded onto sucker rod 23, an additional step in the process may include passing the sucker rod 23 having the molded scrapers 24 thereon back through the surface preparation cabinet 12 where the molded plastic paraffin scrapers 24 are subjected to steam. Molded plastic has a brittleness which may be reduced by moisturizing with steam, so that the strength of the plastic parafiin scrapers 23 are materially improved by this additional step.

The distance between paraflin scrapers on sucker rods varies according to the length of the stroke of the pumping unit used to reciprocate the rods. If a short stroke length is required a shorter distance between paraffin scrapers is necessary so that the total length of the tubing wherein parafiin is likely to be formed is scraped on each cyclie of the upward and downward movement of the sucker rods. As an example, if a pumping unit has a stroke of five feet, then the parafiin scraper must be located not more than five feet apart. As a general rule in most oil producing areas in the United States wherein parafiin scrapers are required, the stroke length is in excess of five feet, and so, as a normal standard, five paraffin scrapers are placed on each twenty-five foot sucker rod. One of the novel features of this invention is the provision of slide rails 25 supporting the surface preparation cabinet 12. Surface preparation cabinet 12 may be moved toward or away from the molding machine 14 so that the distance between the area on the sucker rod within the surface preparation cabinet 12 and the area of the sucker rod 23 within the molding machine 14 is equal to the required spacing between adjacent paraflin scrapers 24. In this way, as a paraffin scraper 24 is being molded on a sucker rod 23 within molding machine 14,

the area to receive the subsequent paraffin scraper 24 is being prepared in surface preparation cabinet 12.

This novel feature of providing means whereby the distance between surface preparation cabinet 12 and molding machine 14 may be varied permits paraffin scrapers to be applied very rapidly to a sucker rod. As previously mentioned, it takes approximately two minutes to injection mold a plastic parafiin scraper onto a sucker rod. The mechanism of this invention is designed such that this is approximately the amount of time required to prepare the surface of the sucker rod in surface cleaning cabinet 12. In this manner, completely outfitting a twenty-five foot sucker rod with five parafiin scrapers can be accomplished in approximately ten to twelve minutes.

The configuration of parafiin scrapers applied by the methods of this invention depends, of course, upon the configuration of the mold used in injection molding machaine 14. Although a great variety of mold shapes may be utilized, three superior configurations are indicated in FIGURES 3A, 4A, and 5A. The configuration of 3A utilizes a multiplicity of integrally formed spiral blades 26. Blades 26 are integrally molded with body portion 28 of the plastic paraffin scraper 24 which is molded and similtaneously bonded to sucker rod 23. The number of helix or spiral blades 26 will depend, of course, upon the degree of spiral of each blade. If only two blades 26 are utilized, the spiral-of each blade must extend through one hundred and eighty degrees so that a complete scraping of the interior wall of the tubing occurs on each passage of the paraffin scraper 23. If three blades 26 are utilized, each blade 26 must spiral a total of one hundred and tweny degrees, and if four blades 26 are utilized, each blade must spiral ninety degrees. The configuration shown, as indicated in end view of FIGURE 3B, utilizes four blades 26, and therefore, each blade spirals ninety degrees.

The distadvantage of the paraffin scraper of FIGURE 3A is that as sucker rods having this type scraper afiixed thereto pass through fluid, for instance on the downward stroke of the sucker rod when the fluid within the tubing is more or less stationary, passage of fluid past the blades 26 creates a rotary torque on the sucker rods. Although sucker rods are suspended in a non-rotary position at the surface, the flexibility of the rods, particularly on a long string as is encountered in a deep well, permits a certain rotary movement which has a tendency to un-- screw couplings and to unscrew the sucker rods from the pump, etc. To overcome this, plastic paraffin scrapers having configurations such as FIGURE 3A must be provided wherein the helical blade 26 spirals one direction in part of the parafiin scrapers 23, andin the opposite direction in the other part of the parafiin scrapers 23, so that the rotary force applied by the movement of the parafiin scrapers through the fluid column within the well tubing is counter-acted. Typically, this configuration of plastic parafiin scraper will be applied to sucker rods such that scrapers having right hand spirals are alternated with scrapers having left hand spirals throughout the entire length of the sucker rod string.

FIGURE 4A indicates a paraffin scraper configuration wherein blades 26 are parallel to the axis of sucker rod 23. This eliminates any tendency to rotate the sucker rods, but in order to scrape the full internal circumference of the tubing, some provision must be made to rotate the sucker rods 23. This is usually accomplished by a rod rotator positioned on the surface so that the rods are gradually rotated by the effect of the pumping stroke, a few degrees each stroke.

The most commonly used types of rod rotators rotate the sucker rods continuously in one direction. The scraper configuration of FIGURE 4A is adaptable for use with such types of rod rotators. An improved arrangement would include the utilization of a rod rotator which rotated first in one direction, then reversed itself and rotated in the opposite direction. When suckerrods are continuously rotated in one direction an objectionable effect is produced tending to unscrew the gas anchor or 7 other elements associated with the pump which objection is overcome by alternating the direction of rotation. The amount of total rotation required depends upon the number of blades 26. When four blades 26 are provided, as in FIGURES 4A and 4B, the sucker rods 23 must be rotated in on direction through ninety degrees, and then rotated in the opposite direction through ninety degrees.

The plastic parafiin scraper 24 of FIGURE 5A is deemed to be a superior design and is an important novel element of this invention. In this configuration each blade 26 forms a double helix. That is, each blade 26 starts out from end to form a helix similar to the arrangement of FIGURE 3A. At the midpoint 32 of parafiin scraper body portion 28 the direction of the helix is reversed, so that the termination of each blade 26 is substantially in line with its beginning at the opposite end. Each blade 26 spirals to the midpoint 32 of body portion 28, an equivalent to the number of degree spacing between the starting points of each blade 26. Thus, if there are four blades 26, as indicated in FIGURE 5A and FIGURE 5B, each blade 26 will spiral from the beginning at one end ninety degrees to midpoint 32. If only three blades 26 are utilized, then each blade 26 must spiral from the beginning at one end to midpoint 32 a total of one hundred and twenty degrees.

The advantages of the improved and novel paraffin scraper configuration of FIGURE 5A is that it does not have to be rotated in order to sweep the complete internal circumference of tubing clean as it passes through the tubing, and on the other hand, there is no rotary torque imparted to the sucker rods 23.

Other styles or configurations of plastic parafiin scrapers adaptable for direct injection molding to sucker rods will suggest themselves and such other configurations are within the purview of this invention.

An alternate embodiment of this invention is shown in FIGURES 6 through 11. This embodiment is adaptable to the utilization of the mechanisms of FIGURE 1, except that in place of an injection molding machine, a thermoplastic fusing machine 14 is utilized. That is, instead of directly molding plastic scrapers 24 to the sucker rod 23, premolded plastic scraper halves 33 are positioned together to encompass the rod 23 in an area wherein the surface has been properly prepared in surface preparation cabinet 12, and thermofused under heat and pressure to the sucker rod 23. FIGURE 6 indicates a'side view of a typical premolded paraifin scraper half 33 adaptable for use according to this alternate embodiment of the invention. Each premolded plastic half includes a blade 26 integrally formed with body portion 28. In this instance blade 26 is a one hundred and eighty degree helix.

Side view of two premolded plastic parafiin scraper halves 33 are shown in FIGURES 7 and 8. The body portion 28 of each premolded plastic paraffin scraper half 33 is semi-tubular in configuration so that when two of the premolded plastic paraffin scraper halves 33 are placed in abutment a tubular opening is formed of an internal diameter substantially equal to the external diameter of the sucker rod 23 to which they are to be applied. Each of the body portions 23 has integrally formed therewith interlocking step portions 34. These match opposite recessed step areas 36, so that when abutted a complete cylindrical body portion is formed. Interlocking step portions 34 and matching recessed step areas 36 are integrally formed in each premolded plastic paraffin scraper half 33 to provide increased area of contact between two abutting halves 33 and thereby increase the bonded tenacity with which they adhere to each other after bonding to a sucker rod.

Premolded plastic parafiin scraper halves 33 are affixed to a sucker rod 23 by first coating an area of the sucker rod 23 which has been cleaned and otherwise prepared as previously described, with a suitable thermosetting resin. Two premolded plastic paraffin scraper halves 33 are then positioned in abutting arrangement encompassing the coated portion of thesucker rod 23 and subjected to heat and pressure in thermofusing machine 14. The premolded plastic parafiin scraper halves 33 are thereby thermofused to each other and simultaneously to the sucker rod 23.

Referring to FIGURE 9, grooves 38 are formed in the internal diameter of each premolded plastic parafiin scraper half 33. Adjacent grooves 38 provide therebetween gripping lugs 40. This configuration permits the concentration of pressure exerted by thermofusing machine 14 on the gripping lugs 40 to that they are more securely thermofused to the sucker rod 23. The grooves 38 provide areas wherein excessive thermosetting resin may accumulate to further insure a thorough bond of the prelmzrglded plastic parafiin scraper halves 33 to the sucker r0 FIGURES 10 and ll show in cross-section premolded A plastic paraflin scraper halves 33 thermofused to a sucker rod 23. The interlocking step portions 34 in each case abut with recessed portions 36 to form, when fused together, an integral tubular body portion 28.

In this disclosure the term thermoplastic is used in its broadest sense and includes any moldable or castable plastic materials and thermosetting resins. Included in this type of plastic materials are nylon compounds, polycarbonates, polypropylene, melamine formaldehyde and polyesters. These compounds may be used unfilled or filled with glass fibers, asbestos fibers or synthetic fibers. The term plastic molding machine as herein used includes any type of molding machine for molding or therrnofusing plastic components as in the applications herein set out, and includes injection molding machines, vacuum molding machines and machines adaptable for thermofusing premolded plastic components.

Although this invention has been described with a certam degree of particularity, it is manifested that many changes may be made in the details of construction without departing from the spirit and scope of this disclosure.

I claim: A method of providing a series of parafiinscrapers on a sucker rod comprising the steps of:

positioning a first portion of the length of said rod in a surface preparation cabinet;

treating said first portion of said sucker rod within said surface preparation cabinet to obtain a clean, scalefree, surface thereof;

longitudinally moving said sucker rod to position said first portion of said sucker rod having been treated in said surface preparation cabinet into a segmented mold and thereby simultaneously moving a second portion of said sucker rod into said surface preparat10n cabinet, said segmented mold encompassing said first portion of the length of said sucker rod having previously been treated, said mold positioned to encompass said sucker rod having a cavity with a configuration defining the ultimately desired paraffin scraper configuration; in ecting thermoplastic material into said mold cavity whereby said thermoplasitc surrounds and adheres to said first portion of said sucker rod encompassed by said mold cavity and fills said mold cavity; concurrently treating said second portion of said sucker rod within said surface preparation cabinet to obtain v a clean, scale free, surface thereof; cooling said thermoplastic material within said mold until said thermoplastic material solidifies; longitudinally displacing said sucker rod to position said second portion of said sucker rod having been treated in said surface preparation cabinet into said segmented mold and simultaneously thereby moving a third portion of said sucker rod into said surface preparation cabinet; and

repeating the steps until said sucker rod has been longitudinally moved the full length thereof through said 9 10 surface preparation cabinet and said mold whereby 3,047,934 8/1962 Mayner 264-265 a series of spaced apart paraflin scrapers are formed 3,063,760 11/ 1962 Gifford. onto said sucker rod. 3,065,795 11/1962 Bartel 166176 3,077,002 2/1963 Warnken 1836 XR References Cited by theAExammer 5 FOREIGN PATENTS 1 157 572 5 fi P TENTS 773,837 5/1957 Great Britain.

I 1 08116 2,266,432 12/1941 Morin et a1. OTHER REFERENCES 2,358,259 9/1944 Siedschlag. Structural Adhesives, London, Lange, Maxwell, and 2,465,656 3/1949 Morin 264-251 10 Springer, 1952, pp. 153-155. 2,476,588 7/1949 Dreher. 2,716, 23 1955 Tater 1 3 XR ALFRED L. LEAVITT, Primary Examiner. 2,835,016 5/ 1958 Dixon. EARL M. BERGERT, ROBERT F. WHITE, Examiners. 2,863,704 12/1958 Hlllrnan 166176 XR 2 937 409 5/19 0 Cole 1 3 XR 15 W. 'B. WALKER, L. S. SQUIRES, ASSISIHHI Examiners. 

